1. Field of the Invention
The present invention relates to a liquid crystal composite material, a liquid crystal display device using this liquid crystal composite material, and a new ter phenyl derivative which can be used favorably in the liquid crystal composite material.
2. Description of Related Art
A liquid crystal display device is a device which uses the electrooptical effects of liquid crystals. The liquid crystal phases used therein include the nematic phase, the cholesteric phase and the smectic phase. At present, the most widely used display methods are the twisted nematic form (hereafter called TN) which uses the nematic phase, or the super twisted nematic form (hereafter called STN) which further enlarges the twisting angle. In large-capacity displays, active matrix displays in which switching devices are placed at each pixel electrode are used. The switching devices are matrix driven and switching of the respective pixel electrodes is conducted through the switching devices. Liquid crystal display devices offer the following advantages:
1. The unit can be made small and thin; PA0 2. The drive voltage is low, as is power consumption; and PA0 3. The user's eyes do not tire even after a long period of usage because the displays are light-receiving devices. PA0 1. Having no coloration, and being stable thermally, electrically, optically and chemically. PA0 2. Having a wide range of practical use temperatures. PA0 3. Having fast electrooptical response speed. PA0 4. Having low drive voltages. PA0 5. Having rapid start-up of voltage-optical transmittance properties, with the temperature dependence of the threshold voltage (hereafter called V.sub.th) being small. PA0 6. Having a wide range of visual angles.
Because of these advantages, liquid crystal display devices have been applied to wristwatches, electronic calculators, audio equipment, various measuring instruments and the dashboards of automobiles and the like. More recently, these devices have been applied to displays for personal computers and word processors and to color televisions and other displays with extremely large numbers of pixels, and are viewed as substitutes for CRTs. Thus, liquid crystal display devices are being applied to a wide range of fields, and the range of applications will likely continue to expand in the future. It is probable that the properties required of liquid crystal materials will also change accompanying this expansion, with the properties listed below serving as concrete examples.
Of these properties, numerous liquid crystals are known which satisfy property 1, but liquid crystal compounds with simple components satisfying properties 2 through 6 are not known. In order to satisfy these properties, numerous liquid crystal composite materials are used wherein nematic liquid crystal compounds or non-liquid crystal compounds are mixed. Because liquid crystal display devices are used in wristwatches, electric calculators and personal computer and word processor displays, a low drive voltage is particularly sought from among these properties.
In addition to analog watches which use needles and digital watches which are equipped with liquid crystal display devices, recent watches have been developed which are hybrid watches having small liquid crystal windows because of the diversified information that is to be displayed, as well as bi-layer watches in which a liquid crystal display device overlaps the surface of an analog watch using a needle (for example, see Japanese Laid-Open Patent Publication Sho 54-94940). In the field of clocks and electronic notebooks, multi-functional devices are being developed which have various functions. For these kinds of applications, the development of a display device which is transparent and bright in a non-magnetic field is anticipated. Accompanying these kinds of applications, reflective-type display devices which are bright and do not use polarizing plates are being developed. For example, a mode which is transparent in an impressed electric field and dispersed under no impressed electric field (abbreviated PDLC; see Japanese Laid-Open Patent Publication Sho 58-501631) and devices which are dispersed under an impressed electric field and either absorb light or are transparent under no impressed electric field (abbreviated reverse PDLC; in Japanese Laid-Open Patent Publication Hei 4-227684 as gel network form, in Japanese Laid-Open Patent Publication 5-119302 as the granule orientation dispersion form; and in U.S. Pat. No. 4,994,204 as the liquid crystal droplet dispersion form) have been developed.
In information equipment fields including wristwatches, the trend has been toward making devices smaller and portable, and display devices for mounting on these devices are being sought which have low power consumption. These types of portable information display equipment and information processing equipment generally require batteries making longevity of the battery when using the devices an extremely important topic. Consequently, devices have been developed which include solar cells. For example, in Japanese Laid-Open Patent Publication Sho 53-38371, the aim is to conserve space by combining a liquid crystal display device and a solar cell. In Japanese Laid-Open Patent Publication Sho 63-106725, an example is provided with a solar cell placed near a liquid crystal display device and wherein the display device is used in which the liquid crystal is dispersed. Regardless of whether the device uses a solar cell or is driven by a battery, display devices with low power consumption are required.
Conventional liquid crystal display devices of the type having bright polymer-dispersion without using light-scattering boards (hereafter, abbreviated PDLC) have the problem that the drive voltage is high. When PDLC was first developed, the drive voltage was several dozen volts. At present, the drive voltage has dropped below 10 V, but even then 5 V is necessary, making a PDLC with as small a drive voltage as possible desirable.
Accordingly, it is an objective of the present invention to provide 1) a liquid crystal composite material with which the drive voltage of liquid crystal display devices and of liquid crystal display devices of polymer-dispersion type can be lowered; 2) liquid crystal display devices and polymer-dispersion type liquid crystal display devices in which the drive voltage has been lowered; and 3) new compounds which can be used favorably in these kinds of liquid crystal display devices.